1. Field of the Invention
This invention relates to a cruising control apparatus which is used for running an automotive vehicle at a desirably preselected speed without operating an accelerator pedal by automatically controlling a throttle valve.
2. Description of the Prior Art
Heretofore, an apparatus with following function has been known a cruising control apparatus for automatically running the automotive vehicle at the desirably preselected speed.
Namely, in the conventional cruising control apparatus, a set coast switch of a command switch is switched on by a driver's operation when the vehicle speed attains desired speed between the predetermined minimum and maximum speeds suitable for the automatic constant speed cruising while the vehicle is travelling, thereby producing a cruise command signal, and the vehicle speed signal of the present vehicle speed generated from the vehicle speed sensor at the time of switching off the set coast switch is stored in a vehicle speed signal storage means according to the off-operation of the set coast switch. After this, a deviation between the vehicle speed signal generated from the vehicle speed sensor and the memory vehicle speed signal stored in the vehicle speed signal storage means and an acceleration obtained from a change rate of the vehicle speed signal generated from the vehicle speed sensor within a definite period of time are computed successively, and an actuator is actuated by being supplied with an electric current through an actuator switching means so that the present vehicle speed may correspond to the memory vehicle speed, thereby opening or closing a throttle valve of an engine of the automotive vehicle.
A microcomputer in the cruising control apparatus is always monitored by a watch dog signal discriminating means connected to a watch dog signal output means which is so designed as to generate always a pulse signal with a period predetermined according to a program of the microcomputer. If the pulse signal from the watch dog signal output means stops unexpectedly during the constant speed cruising control, the watch dog signal discriminating means discriminates that the microcomputer malfunctions, and makes the actuator switching means in an OFF-state by actuating a prohibiting means so that the actuator may not actuate the throttle valve infallibly in a case of malfunction of the microcomputer.
In the conventional cruising control apparatus, the actuator is controlled so as to be made in the non-working state by the watch dog signal discriminating means through the actuator switching means when the pulse signal from the watch dog signal output means discontinues as mentioned above, and the watch dog signal output means generates the pulse signal always even when the present vehicle speed is lower than the lower limit or higher than the upper limit of the automatic cruising control.
Therefore, there is a problem in that it is not always safe absolutely from the view point of controlling the actuator, and it is desired to overcome this problem.